Vector3.MoveTowards

Description

Moves a point current in a straight line towards a target point.

The value returned by this function is a point maxDistanceDelta units closer to a target/ point along a line between current and target. If the target is closer than maxDistanceDelta/ then the returned value will be equal to target (ie, the movement will not overshoot the target). Negative values of maxDistanceDelta can be used to push the point away from the target.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Transform target;
    public float speed;
    void Update() {
        float step = speed * Time.deltaTime;
        transform.position = Vector3.MoveTowards(transform.position, target.position, step);
    }
}